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Avalanche Forecast

Archived

Mar 18th, 2016–Mar 19th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Mt Hood.

Check the forecast for a mixed bag of spring avalanche problems and evaluate snow and terrain carefully on Saturday.

Detailed Forecast

Increasing mid and high clouds should be seen on Saturday. The best chance of some light rain or snow showers should be over the Olympics. Any rain and snow amounts will be light and should not cause a change in snow conditions. East winds should decrease over the Cascade crest and in the Cascade passes on Saturday.

The avalanche forecast won't change much from Friday.

Loose wet avalanches may still be possible on steeper solar aspects on Saturday. Loose wet avalanches may start small but could have the ability to entrain recent moist snow in mainly on steep solar terrain. High clouds Friday night may limit a refreeze of surface snow by Saturday morning.

Storm winds 3/13-15 likely built wind slab on lee aspects in the upper elevations of the above treeline band. This wind slab will mostly likely be found on NW-SE facing slopes. But east winds the past couple days will also have built wind slab on northwest to southwest aspects in places along the Cascade crest and in the Cascade passes. Hence the the wind slab avalanche problem will be indicated on all aspects in the near and above treeline.

Wind slab may also be locally possible in the below treeline on west slopes in areas that had east winds the past couple days. Firm wind transported snow and snowpack cracking can be good signs of wind slab layers.

Recently formed cornices have grown large and can become sensitive when it is warm and sunny. Avoid areas on ridges or summits where there may be a cornice and avoid slopes below cornices in the spring.

Although it won't be listed as an avalanche problem avoid areas below steep slopes or rock faces where unusual glide avalanches can release unexpectedly.

Snowpack Discussion

Weather and Snowpack

Storms moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels. Two deep surface low-pressure systems moved across the Olympic Peninsula last week with the first passing last Thursday 3/10, and the next on Sunday, 3/13. These systems caused very stormy weather.  

Cool and showery weather Monday and Tuesday with  prolonged westerly winds deposited additional snow at lower snow levels.

Storm totals on Mt Hood were impressive with about 4 feet of new snow accumulating over about 4 days ending Wednesday morning 3/16 at the NWAC Mt. Hood Meadows and Timberline stations!  

The mid and lower snow pack at Mt Hood should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The Mt Hood Meadows pro-patrol on Sunday 3/13 reported stormy conditions with widespread wind and storm slab of 6-12 inches on all aspects in the area, easily triggered by ski cuts and running on a crust buried on Thursday 3/10.

A report for Newton Canyon via the NWAC observations page for Monday 3/14 indicated stormy weather and numerous ski triggered 3-10 inch storm slabs.

On Monday and again Tuesday 3/14-15, control performed by Mt. Hood Meadows pro-patrol produced extensive and sensitive wind and storm slab avalanches triggered by ski cuts in lower elevation slopes and explosives in wind loaded terrain. Avalanches were greatest on N-E facing terrain. Loose wet slides were releasing on solar aspects by Tuesday afternoon below treeline.

On Wednesday 3/16, the Meadows pro-patrol were still finding hard wind slab of up to a foot above treeline on the usual lee aspects with a rising hazard of loose wet avalanches in steeper terrain below treeline due to warming and sunbreaks.

On Thursday 3/17 the Meadows pro-patrol reported strong east winds but not much snow available for transport. Small loose wet avalanches and rollerballs were seen only on direct solar slopes.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.